Plasma Group Science

Thermal Spray Coating

 

Thermal Spraying Application Illustrations

Plasma Coating Process

High Velocity Oxy-Fuel Process

Flame Spray Process

Flame Spray Wire Process

Plastallium 212

 

High Velocity Oxy-Fuel Process


Introduction

HVOF spraying has been developed principally to produce high quality metal and carbide coatings equivalent to the D - Gun process and with superior properties to conventional flame spray processes

Main Applications

    • Rotary knife blades
    • Aero engine parts
    • Gate valves
    • Pistons
    • Shafts.

Process Description

The HVOF process typically uses oxygen and hydrogen as the fuel gases to give coatings of the highest quality. Mixing of the gases occurs inside the gun and the externally ignited flame reaches a temperature of about 2700ºC. Powder material is injected through the flame and the molten particles projected at velocities approaching 2000 metres per seconds on to the workpiece. Precise control of all spraying parameters and powder feed rates, and the use of a robot to precisely position the gun, enables high quality coatings to be repeated on a large variety of different components.

General Coating Characteristics

    • high bond strength (83 MPa - 12000 p.s.i.). 
    • high density, low porosity. 
    • low oxide. 
    • high hardness (DPH 500 1000 - 1300 for WC/Co). 
    • fine as sprayed texture, able to be ground or lapped to a fine finish (0.1-0.2 microns). 
    • excellent resistance to wear by abrasion, erosion or fretting.

Available Coatings

At present these consist mainly of coatings based upon Tungsten Carbide/Cobalt -and Chrome Carbide/Nickel, as well as Stainless Steel,  Aluminium Bronze and others.

Coating Characteristics Typical Applications
Tungsten Carbide / Cobalt (88/12) Macrohardness - Rc 64 - 66
Microhardness - DPH300 1015 -1300
Tensile Bond Strength - 83MPa(12000psi)
Surface Texture 
- as sprayed - 2.5 - 4 microns
- as ground - 0.05 - 0.1 microns		 Shafts and pistons in high abrasive wear environments. Rotary cutting knives to improve edge life and cutting performance.
Chromium Carbide/Nickel Chrome (93/7) Macrohardness - Rc 53 - 57
Microhardness - DPH300 600 - 650
Tensile Bond Strength - 73MPa(10500psi)
Surface Texture 
  - as sprayed - 5 - 6 microns
- as ground - 0.2 - 0.3 microns

Used in temperature range 540 - 910°C where resistance to wear by fretting or particle erosion is required.

Possible applications include piston guides, expansion joints and compressor seals.

Chromium Carbide/Nickel Chrome (75/25) Macrohardness - Rc 55
Microhardness - DPH300 700 - 800
Tensile Bond Strength - 83MPa(12000psi)
Surface Texture 
- as sprayed - 5 - 9 microns
- as ground - 0.4 - 0.5 microns

Recommended to resist high wear by fretting or particle erosion at temperatures in the range 540 - 815°C.

Possible applications include turbine seal rings, fuel rod mandrels and hot crushing rolls.

Cobalt/Molybdenum/Chromium (62,28,8) Macrohardness - RC 53 - 57
Microhardness - DPH300 500 - 700
Oxide Content - 10%
Tensile Bond Strength - 68MPa(10000psi)
Surface Texture 
- as sprayed - 5 - 9 microns
- as ground - 0.1 - 0.2 microns		 Used up to 700°C to resist corrosion and oxidation. Also has excellent resistance to galling and wear by rubbing. Possible applications in engine components where fretting or poor lubrication is a problem. For example, aft and forward seals in low pressure nozzles or valve seats.  
Iron/Molybdenum/Carbon (95,3,2) Macrohardness - RC 48 - 52
Microhardness - DPH300 625 - 725
Oxide Content - 20%
Tensile Bond Strength - 59MPa(8500psi)
Surface Texture 
- as sprayed - 5 - 9 microns
- as ground - 0.1 - 0.2 microns		 For use below 340°C as a hard bearing surface where resistance to wear by hard surfaces or abrasive grains is required.Possible applications include bearing journals,

 

 

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Plasma Coatings Limited

Unit 3, Whitecross Road Industrial Park

Tideswell, North Derbyshire

SK17 8PY, England

e-mail : info@plasma-group.co.uk

Tel : +44 (0) 1298 873700, Fax : +44 (0) 1298 873708

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